1. Field of the Invention
The present invention relates to a medical device for placing an embolic coil at a preselected location within a vessel of the human body, and more particularly, relates to a flexible delivery member having a heating element and a heat responsive coupling member at the distal tip of the delivery member for holding the embolic coil in order to transport the coil to a desired position within the vessel and release the embolic coil at that position.
2. Description of the Prior Art
For many years flexible catheters have been used to place various devices within the vessels of the human body. Such devices include dilatation balloons, radiopaque fluids, liquid medications and various types of occlusion devices such as balloons and embolic coils. Examples of such catheter devices are disclosed in U.S. Pat. No. 5,108,407, entitled xe2x80x9cMethod And Apparatus For Placement Of An Embolic Coilxe2x80x9d; U.S. Pat. No. 5,122,136, entitled, xe2x80x9cEndovascular Electrolytically Detachable Guidewire Tip For The Electroformation Of Thrombus In Arteries, Veins, Aneurysms, Vascular Malformations And Arteriovenous Fistulas.xe2x80x9d These patents disclose devices for delivering embolic coils to preselected positions within vessel of the human body in order to treat aneurysms, or alternatively, to occlude the blood vessel at the particular location.
Coils which are placed in vessels may take the form of helically wound coils, or alternatively, may be random wound coils, coils wound within other coils or many other such configurations. Examples of various coil configurations are disclosed in U.S. Pat. No. 5,334,210, entitled, xe2x80x9cVascular Occlusion Assembly; U.S. Pat. No. 5,382,259, entitled, xe2x80x9cVasoocclusion Coil With Attached Tubular Woven Or Braided Fibrous Coverings.xe2x80x9d Embolic coils are generally formed of radiopaque metallic materials, such as platinum, gold, tungsten, or alloys of these metals. Often times, several coils are placed at a given location in order to occlude the flow of blood through the vessel by promoting thrombus formation at the particular location.
In the past, embolic coils have been placed within the distal end of the catheter. When the distal end of the catheter is properly positioned the coil may then be pushed out of the end of the catheter with, for example, a guidewire to release the coil at the desired location. This procedure of placement of the embolic coil is conducted under fluoroscopic visualization such that the movement of the coil through the vasculature of the body may be monitored and the coil may be placed at the desired location. With these placements systems there is very little control over the exact placement of the coil since the coil may be ejected to a position some distance beyond the end of the catheter.
Numerous procedures have been developed to enable more accurate positioning of coils within a vessel. Still another such procedure involves the use of a glue, or solder, for attaching the embolic coil to a guidewire which, is in turn, placed within a flexible catheter for positioning the coil within the vessel at a preselected position. Once the coil is at the desired position, the coil is restrained by the catheter and the guidewire is pulled from the proximal end of the catheter to thereby cause the coil to become detached from the guidewire and released from the catheter system. Such a coil positioning system is disclosed in U.S. Pat. No. 5,263,964, entitled, xe2x80x9cCoaxial Traction Detachment Apparatus And Method.xe2x80x9d
Another coil positioning system utilizes a catheter having a socket at the distal end of the catheter for retaining a ball which is bonded to the proximal end of the coil. The ball, which is larger in diameter than the outside diameter of the coil, is placed in a socket within the lumen at the distal end of the catheter and the catheter is then moved into a vessel in order to place the coil at a desired position. Once the position is reached, a pusher wire with a piston at the end thereof is pushed distally from the proximal end of the catheter to thereby push the ball out of the socket in order to release the coil at the desired position. Such a system is disclosed in U.S. Pat. No. 5,350,397, entitled, xe2x80x9cAxially Detachable Embolic Coil Assembly.xe2x80x9d One problem with this type of coil placement system which utilizes a pusher wire which extends through the entire length of the catheter and which is sufficiently stiff to push an attachment ball out of engagement with the socket at the distal end of the catheter is that the pusher wire inherently causes the catheter to be very stiff with the result that it is very difficult to guide the catheter through the vasculature of the body.
Another method for placing an embolic coil is that of utilizing a heat releasable adhesive bond for retaining the coil at the distal end of the catheter. One such system uses laser energy which is transmitted through a fiber optic cable in order to apply heat to the adhesive bond in order to release the coil from the end of the catheter. Such a method is disclosed in U.S. Pat. No. 5,108,407, entitled, xe2x80x9cMethod And Apparatus For Placement Of An Embolic Coil.xe2x80x9d Such a system also suffers from the problem of having a separate, relatively stiff element which extends throughout the length of the catheter with resulting stiffness of the catheter.
Still another method for placing an embolic coil is disclosed in co-pending U.S. patent application Ser. No. 09/177,848, entitled, xe2x80x9cEmbolic Coil Hydraulic Deployment System,xe2x80x9d filed on Oct. 22, 1998 and assigned to the same assignee as the present patent application. This patent application discloses the use of fluid pressure which is applied to the distal tip of the catheter for expanding the lumen of the catheter in order to release the embolic coil.
The present invention is directed toward a vascular occlusion coil deployment system for use in placing an embolic coil at a preselected site within a vessel which includes an elongated flexible positioning member having a lumen extending therethrough. An elongated flexible delivery member having a lumen extending therethrough is slidably positioned within the lumen of the positioning member. A heating element is affixed to the distal end of the delivery member and a heat responsive coupling member adhesively bonds the embolic coil to the heating element. The heating element is adapted to be coupled to a source of energy through an energy transmission conductor which extends through the lumen in the delivery member. The heat responsive coupling member, bonding the heating element to the embolic coil, exhibits the characteristic of softening and yielding upon being heated. When energy is applied through the conductor to the heating element, the heating element causes the heat responsive coupling member to yield to thereby release the embolic coil at the preselected site.
In accordance with another aspect of the present invention, the heating element takes the form of resistive heating coil. At least a portion of this resistive heating coil is bonded to the interior of the heat responsive coupling member to thereby directly apply heat to the coupling when the heating coil is supplied with electrical energy.
In accordance with still another aspect of the present invention, the vascular occlusion coil deployment system for use in placing an embolic coil at a preselected site within a vessel includes an elongated flexible positioning member having a lumen extending therethrough. An elongated flexible delivery member is slidably positioned within the lumen of the positioning member. A heating element is affixed to the distal end of the delivery member and a heat responsive coupling member adhesively bonds the embolic coil to the heating element. The heating element is adapted to be coupled to a source of energy through an energy transmission conductor. The energy transmission conductor extends from the proximal end to the distal end of the delivery member through the lumen of the positioning member and is coupled to the heating element. The heat responsive coupling member, bonding the heating element to the embolic coil, exhibits the characteristic of softening and yielding upon being heated. When energy is applied through the conductor to the heating element, the heating element causes the heat responsive coupling member to yield to thereby release the embolic coil at the preselected site.
In accordance with still another aspect of the present invention, the energy transmission conductor takes the form of two electrical conductors which extend through the lumen of the delivery member and are connected to the resistive heating coil for applying electrical energy to the coil to thereby cause the coil to become heated.
In accordance with still another aspect of the present invention, the heating element is disposed within a lumen of the embolic coil. The heat responsive coupling member bonds the embolic coil to the heating element. When the heating element is energized the heat responsive coupling member heats. Upon heating the heat responsive coupling member softens thereby reducing its yield strength. This allows the heating element to be retracted into the positioning member breaking the heat responsive coupling member to release the coil.
In accordance with still another aspect of the present invention, the heat responsive coupling member is comprised of a hot melt adhesive. Other suitable materials include low melting temperature metals and metal alloys such as solder. Other suitable materials are those whose yield strength decreases by at least 50 percent when heated to about 65 degrees Celsius.
These aspects of the invention and the advantages thereof will be more clearly understated from the following description and drawings of a preferred embodiment of the present invention: